1. Field of the Invention
This invention includes the method for producing high coercivity FePt--Si.sub.3 N.sub.4 granular composite thin films that may be used for high-density magnetic recording media.
2. Description of the Prior Art
For a long time now, the most important problem in magnetic recording medium has been how to increase its recording density. A high recording density medium needs high coercivity Hc and optimum remnant magnetization Mr for giant magnetic resistance (GMR) and MR read-heads.
At present, the CoCrPtM (M=Ni, Ta, W) alloy thin films are the most widely used magnetic recording materials for hard disk drive, due to their high coercivity (Hc&gt;2800 Oe). However, these alloy thin films have two disadvantages for high recording density applications: (1) media noise is too high, and (2) coercivity is not enough, therefore the recording density can not be increased. For these metallic films, the most significant problem is the noise that results from magnetic exchange coupling between the grains located at the domain transition region (Jian-Gang Zhu, "Transition Noise Properties in Longitudinal Thin Film Media", IEEE Trans. Magn. Vol. 29, no.1, pp.195-200, 1993). On the other hand, if the areal recording density of the metallic film is to be increased, the grain size of the film must be reduced (D. N. Lambeth, E. M. T. Velu, G. H. Bellesis, L. L. Lee, and D. E. Laughlin, "Media for 10 Gb/in.sup.2 Hard Disk Storage: Issues and Status", J. Appl. Phys., 78(8), pp.4496-4501, 1996). However, due to the lack of enough space among grains to reduce the magnetic exchange coupling between the grains, even the grain size of the continuous metallic film is decreased to single-domain size, the high media noise will lead to read-write error and system instability. (E. I. Kondorsky, "On the stability of certain magnetic modes in fine ferromagnetic particles", IEEE Trans. Magn. Vol. 15, no.5, pp.1209-1214, 1986).
To improve the disadvantages of cobalt-based alloy thin films described above, the present inventors have invented high coercivity granular thin films with FePt particles dispersed in a non-magnetically amorphous Si.sub.3 N.sub.4 matrix, for use as a recording media for higher density magnetic recording. Since the magnetic FePt particles in these granular films are isolated, the media noise of the films can be largely reduced. In addition, by using high magnetocrystalline anisotropy FePt particles as recording material, the recording bits of this granular film can be reduced and recording density of the film will be increased, provided that the write ability of magnetic head is strong enough. These granular films for recording media has many other good properties such as oxidization resistance, corrosion resistance and wear resistance due to the magnetic particles being surrounded by an insulator material Si.sub.3 N.sub.4.